Why are only BTC and ETH transfers allowed with Travel rule in the UK?

I'm based in the UK, and I've just discovered, by trying to transfer LTC from a Cex to another Cex, that I can't anymore, because of the recent Travel Rule. Only transfers to non-custodial wallets and transfers of ERC-20 and BTC are allowed.

My question is: why is that? Why can we now only transfer ERC-20 and BTC from Cex to Cex? How is that restriction helping to fight crime and money-laundering? What was the idea behind this? How is blocking those but allowing me to transfer to a hardware wallet help in any way?